1. Field of the Invention
This invention relates to biocidal compositions of 1,2-benzisothiazolin-3-one (BIT) and, more particularly, to stable, VOC-free compositions of BIT which have a neutral pH which is particularly advantageous in use in latex, paint, coating, cosmetic and personal care products.
2. Description of the Prior Art
1,2-benzisothiazolin-3-one (referred to hereinafter as BIT) is an established industrial biocide and is particularly effective in protecting aqueous media against microbiological spoilage. It is particularly effective as a bactericide and is especially suited to the protection of lattices. Thus one of its major uses is as an in-can preservative for the preservation of acrylic and acrylate paint emulsions.
BIT has low aqueous solubility and can cause sensitization in some individuals. Consequently, for ease of handling and to reduce handling risks, it has been formulated as an aqueous dispersion and also as a stable solution in an amine solvent as disclosed in UK Patents 1,191,253 and UK 1,330,531. For some applications, these amine formulations are not attractive and are rarely used for indirect food contact applications, such as for instance for use in water-based adhesives which may be used in the food packaging industry, because the amines are volatile and tend to have an unpleasant odor. Furthermore, amine solutions of BIT may not be suitable for use as biocides in in-can preservation of lattices because amine solvents may cause yellowing of the latex. Amines are also capable of reacting with and deactivating certain biocides and this further limits the use of amine formulations of BIT when used with such biocides.
To avoid these problems associated with amines, BIT is now generally formulated as an alkali metal salt in one or more water miscible solvents such as dipropylene glycol as disclosed in U.S. Pat. No. 4,188,376. Such formulations are stable solutions which withstand freeze-thaw temperature cycling, and, even if frozen recover on warming to regenerate a stable solution. Formulations of this type containing 20% BIT, and 65% dipropylene glycol, the remainder being water, wherein the BIT has been converted to sodium-BIT by reacting 1.1 moles sodium hydroxide with 1 mole BIT as described in Example 1 of said U.S. Pat. No. 4,188,376 have been available commercially for many years as Proxel® GXL (Proxel is a registered trademark of Avecia).
A disadvantage of such formulations is their high pH, normally pH 12 or above, which can cause “pH-shock” and coagulation when added to a medium to be protected, such as an emulsion paint or latex, owing to the different pH of the medium. The high pH is caused by the combination of the amount and type of solvent employed and also the amount of alkali both of which have hitherto been considered necessary to produce stable solutions of sodium-BIT. Indeed, in all the working examples of U.S. Pat. No. 4,188,376 a 10% excess of sodium hydroxide has been used relative to BIT in making the sodium salt.
U.S. Pat. No. 5,558,816 described a BIT composition using dipropylene glycol as the solvent. These compositions had a lower pH (8.9-10) and a lower viscosity (60–180 m Pa.s) than commercial products. However, dipropylene glycol is a volatile solvent and it contributed greatly to the high VOC of the composition.
U.S. Pat. No. 5,585,033 described BIT compositions which contained one or more polyglycol triols, e.g. glycerol ethoxylate or glycerol propoxylate, as the organic solvent, optionally including an organic cosolvent.
U.S. Pat. No. 6,361,788 described BIT compositions free of 5-chloro-2-methylisothiazolin-3-one.
WO 95/00019 described a BIT formulation containing xanthan gum and a dispersant which was free of organic solvents.
Accordingly, it is an object of this invention to provide a new and improved BIT composition which is stable, has a neutral pH, is VOC-free and remains as a homogeneous solution at low temperatures for an extended period of time.
Another object of the invention is to provide BIT compositions which can be included advantageously in latex, paint, coating, cosmetic and personal care products.
These and other objects of the invention will be made apparent from the following description of the invention.